74*245 Motor Driver

H-Bridge Driver

Simple PWM Gen.

Handy Method Measuring RPM

Measuring RPM via Photo reflector

Introduction to Robotic

DC, Stepper,and Servo Motor

Microcontroller Tutorial

Computer Interface
Tutorial
.............more links

BACK NEXT

B. Comparison Section

Before describing the next section we will introduce a new element, the Operational Amplifier (OPAMP).

OPAMP
This device (Fig. 4), has two inputs, VN (the inverting input), and VP (the non-inverting input).

It has one output, VO. The remaining two connections, +VCC and -VCC provide power to the OPAMP. VCC is usually between 12 and 25 V. In our circuit, +VCC is connected to the +9V power supply and -VCC to the ground. We use the OPAMP as a comparator:.

If VP > VN , then V0 = +VCC.
If VP < VN , then V0 = -VCC.

In our case, +VCC=+9V and -VCC=0V(ground)

The integrated circuit (IC) used in this kit contains two OPAMP’s used as comparators. The package (Fig. 5) has 8 pins: 4 inputs, 2 outputs and 2 more pins for +VCC and -VCC.

The robot moves in such a way as to locate itself above a dark line drawn on a white surface. The voltage at pin 3 of the comparator 1 is fixed at +3V because of the voltage divider (we have 9V across the series combination of the 10 and 20kW resistors).

Now let us see what happens if the right photo-interrupter is on a dark region and the left photo-interrupter is on a light region. As we saw in Section A, under this condition VR > VL. This will result in the output of the comparator 2 (pin 7), to be low (a few tenths of a volt). The Amplifier Section connected to pin 7, i.e., TR1 and TR3 (as we will see later) actually work in such a way as to output a large current to the Left Motor when pin 7 is low! This allows the Left Motor to rotate.

At the same time, pin 7 is fed into the pin 2 of comparator 1. Since the voltage at pin 3 of this comparator (the non-inverting input) is held fixed at +3 V, the output (pin 1) will go high (~9V), and the amplifier section, TR2 and TR4 out put very little current to the Right Motor. Therefore it does not rotate. If the left motor operates and the right motor does not, the robot move to the right, until the left photo-interrupter is located on the dark region and the right photo-interrupter on the light region.

The 1k resistors connecting the outputs of the two compatators (pins 7 and 1) to +9V are temporarily there to simulate the rest of the circuit, and are removed when the amplifier section is installed.

BACK NEXT